Rotatable disc type valves having discs rotated into place to close an aperture have long been known. Thus, U.S. Pat. No. 3,512,751--T. W. Fitzgerald--May 19, 1970 shows a typical such valve disc rotated about a pivot axis outside an aperture to cover the aperture opening. This discloses a fast release lever operated valve embodiment. Such valves may be used as fast opening blow-off valves in boilers, etc. as shown in pages 7 to 9 of the Stationary Engineering, Home Study Course by the National Association of Power Engineers.
Another version of these valves, also known as "everlasting" valves is shown in U.S. Pat. No. 3,788,346--T. W. Fitzgerald--Jan. 29, 1974, where the disc itself is given a rotary action as it is being seated by means of a compound lever arrangement and confined housing path.
This type of valve has the advantage of long life because of the shear action of the disc over the mating seat provided about the aperture flow path to be controlled. However, it has been found in accordance with this invention that conventional valves of this type are subject to wear by the fluid flow through the valve resulting in a wear-down of the edges of the control disc. This not only changes valve closure characteristics in the flow path, but also prevents the operation of the shear cleaning action of the disc in passing across the aperture facing, even to the extent of letting particles ride between the disc and facing to lift the valve disc away from its closed position, particularly when the valve disc is biased only by water pressure and covers a single aperture facing. Thus, the life of these valves is materially shortened, and it is therefore an objective of this invention to further improve the long life characteristics of such rotary disc type valves and to correct the wear deficiencies of the prior art.